Method of dosing the arc tube of a mercury-additive lamp



May 28, 1968 J. D. SMITH 3,385,645

METHOD OF DOSING THE ARC TUBE OF A MERCURY-ADDITIVE LAMP Filed March 24, 1966 TO VACUUM AND GAS FILL SYSTEM WITNESSES INVENTOR mu i i WM John 0. Smith w BY 1 n k? ATTORNEY United States Patent 3,385,645 METHOD OF DOSING THE ARC TUBE OF A MERCURY-ADDITIVE LAMP John D. Smith, Caldwell, N.J., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Mar. 24, 1966, Ser. No. 537,169

10 Claims. (Ql. 316-16) ABSTRACT OF THE DISCLOSURE To dose a discharge-sustaining filling into a mercuryadditive type lamp, at least some of the additive metal dosing components are introduced as air-stable oxide, along with mercury at least a part of which is in the form of a halide, along with aluminum as metal. When the lamp is initially operated, the aluminum first reacts with the mercury halide to form aluminum halide. The formed aluminum halide then reacts with the additive metal oxide to form stable aluminum oxide and the desired additive metal halide. The stable aluminum oxide, after formation, does not enter into or affect the discharge.

This invention relates to high-pressure, gas-discharge lamps and, more particularly, to a method for dosing the arc tube of a mercury-additive type of discharge lamp.

High-pressure, mercury-vapor discharge lamps are well known and are used extensively for highway lighting and high-bay factory lighting, as well as numerous other applications. It is well known to modify such lamps by supplementing the mercury discharge with additive metallic halides, such as iodides, which modify the color of the discharge, or increase the lumen output of the lamp, or both. As an example, thallium iodide or sodium iodide or a combination of thallium iodide and sodium iodide can be used to supplement the mercury as a discharge-sustaining filling in order to modify the spectral emission of the resulting lamp and also substantially increase the lumen efliciency of the lamp.

While some of the metallic halides, such as the sodium and thallium iodides, can be readily introduced into the arc tube, it is extremely difficult to introduce many types of metallic halides into the arc tube, since these metallic halides are unstable or hygroscopic in air. The desired metallic halide thus may react with undesired impurities before introduction into the are tube or before the arc tube is sealed. Thus, when it is desired to introduce an unstable metallic halide into the arc tube portion of a discharge device, unwanted impurities are apt to be introduced into the arc tube along with the other dosing constitutents. Such unwanted impurities react with the electrodes, envelope, or other dosing constituents, and thus impair the performance of the resulting lamp.

It is the general object of this invention to provide a method for dosing the arc tube of a mercury-additive discharge device with desired dosing substance which will exist in the operating device as metallic halide, such as the iodide, but which desired dosing substance is unstable in air in the desired halide form.

It is another object to provide a method for dosing the arc tube of a mercury-additive type of discharge device wherein any metal which is desired in the device as a halide can be readily dosed as an oxide into the arc tube.

The foregoing objects of the invention, and other objects which will become apparent as the description proceeds, are achieved by placing into the arc-enclosing envelope portion of a mercury-additive discharge device the dosing charge which includes: (1) a predetermined amount of mercury which is at least partially chemically 3,385,645 Patented May 28, 1968 combined as mercury halide with a predetermined amount of the halogen component of the metal halide which is desired in the lamp, (2) a predetermined amount of selected metal as air-stable oxide, which metal is desired in the device as a selected metal halide, and (3) aluminum in predetermined amount to react with the total oxide in the dosing charge. Thereafter, the arc tube is sealed to complete the fabrication of same. When the device is first operated, the aluminum reacts with the mercury halide in the dosing charge to form aluminum halide. The aluminum halide then reacts with the metal oxide to form the desired metallic halide and aluminum oxide, which is inert in the device as operated.

For a better understanding of the invention, reference should be had to the accompanying drawing, wherein:

FIGURE 1 is. an elevational view of a substantially fabricated but unsealed arc tube portion of a mercuryadditive discharge device, wherein an elongated tubulation projects from the side of the arc tube, with some of the dosing charge included in the arc tube and some in the tubulation;

FIG. 2 is an end view of the arc tube as shown in FIGURE 1 with the aluminum and additive metal oxide included in the arc tube and the mercury-mercury halide included in a receptacle portion of the elongated tubulation;

FIG. 3 illustrates the next step of the dosing operation wherein the tubulation is connected to a vacuum system while the arc-tube is simultaneously baked, with the preliminary sealing or tipping-off operation also shown in FIG. 3;

FIG. 4 illustrates the next and final steps in the dosing operation wherein the mercury-mercury halide in the receptacle portion of the elongated tubulation is first distilled or placed into the envelope, with the tubulation thereafter tipped off at a location proximate the arc tube;

FIG. 5 is an elevational view of a fabricated mercuryadditive type of discharge device which incorporates the fabricated arc tube; and

FIG. 6 is a cross-sectional view taken on the lines VIVI in FIG. 5 in the direction of the arrows.

With specific reference to the form of the invention illustrated in the drawings, the arc tube 10 as shown in FIG. 1 is substantially fabricated and comprises an envelope 12, such as quartz, having operating electrodes 14 positioned proximate either end thereof with a starting electrode 16 positioned proximate one end of the arc tube. Ribbon seals 18 facilitate hermetic sealing through the pressed seal portions of the envelope 12 and lead-in conductors 20 connect to the ribbon seals 18. Such an arc tube construction is generally conventional.

As is shown more clearly in FIG. 2, connected to the envelope and opening therein is an elongated tubulation member 22 which has a receptacle portion 24 depending therefrom. A predetermined amount of aluminum, preferably aluminum powder or foil 26, which has a large surface area, is placed into the envelope 12 through the open tubulation 22, along with a predetermined amount of selected metallic oxide 28. Into the depending tubulation receptacle portion 24 is placed a predetermined amount of mercury which is at least partially chemically combined as mercury halide with a predetermined amount of halogen component of the selected metal halide as desired in the arc tube.

In the next step of the fabricating operation, as shown in FIG. 3, the end of the elongated tubulation 22 is connected to a conventional gas-filling and vacuum system (not shown) and the arc tube 10 heated by a conventional oven 32 in order that substantially all impurities are removed therefrom. The envelope 12 is then charged with a predetermined pressure of inert, ionizable starting gas by the gas-fill system, after which the tubulation 22 is tipped off at a location remote from the envelope with a standard gas-air tipping torch 34. An example of a suitable gas filling is argon at a pressure of 25 torr.

In FIG. 4 is shown the next steps of the fabricating operation wherein the mercury-mercury halide charge 30 is distilled from the depending tubulation portion 24 into the envelope 12 by heating this mercury charge with a conventional gas-air burner 36. This mercury-mercury halide charge will vaporize and condense in the envelope 12. Thereafter, the envelope 12 is sealed or tipped-off by heating the tabulation 22 at a point proximate the envelope 12 by the conventional gas-air tipping torch 34.

The completed lamp 38, as shown in FIGS. 5 and 6, incorporates the fabricated arc tube and the lamp generally comprises a radiation-transmitting, sealed, outer envelope 40 which is spaced from and surrounds the arc tube 10. The electrical lead-in conductors are electrically connected in conventional fashion to the lamp base 42. The are tube 10 is supported within the outer envelope 40 by a conventional supporting frame 44 and a starting resistor 46 connects to the starting electrode 16, as is well known in the art. To facilitate sealing and electrical connection to the arc tube 10, a conventional stem-press arrangement 48 is used.

As a specific example, the distance between the operating electrodes 14 is approximately 70 mm. and the arc tube 10 encloses a volume of approximately 22.5 cc. After the lamp has been operated for a short time, the mercury charge will all be metallic mercury, which as an example is present in amount of 66 milligrams to provide the lamp with an operating potential of approximately 135 volts. The additive metal will be present as the iodide after the lamp has been operated for a short time. The metal iodide is normally included in amount greatly in excess of that amount of additive metal iodide which is vaporized during operation of the lamp. Preferably, the volume between the arc tube 10 and the surrounding envelope is substantially evacuated, although an insert gas filling such as nitrogen may be used. Such a lamp as described hereinbefore is designed to operate with a wattage input of 400 watts, although this may be varied considerably depending upon lamp design.

The oxides of most metals are relatively stable in air and can be readily handled without introducing substantial contamination therein. The halides of many metals, in contrast, are relatively unstable or hygroscopic in air. Examples of metals which are relatively stable in air in the oxide form, but which are not stable in air in the halide form are thorium, tantalum, vanadium, neodymium, gadolinium, uranium, niobium, yttrium, Samarium, ytterbium, europium, indium, terbium, scandium, dysprosium, holmium, erbium, praseodymium, titanium, gallium, hafnium, iridium, lanthanum, magnesium, cerium, palladium, rhenium, rhoidium, ruthenium, and zinc. Any of the foregoing metals, or any mixtures thereof, may be readily handled in the oxide form and introduced as such into the envelope in accordance with the present method.

The mercury is selected to be present in predetermined amount in accordance with the predetermined pressure of mercury vapor which is desired in the operating device to provide the proper voltage drop during operation. In accordance with the present invention, during dosing at least a part of this mercury is combined with the halogen as desired in the finished device. The halogen need not be present in such amount as to react stoichiometrically with the metal oxide to form the selected metal halide, since a slight excess of halogen may be desired or a slight deficiency of halogen may be desired depending upon the desired operation for the device. The aluminum, which is preferably in powdered or foil form to promote reaction with the halide, is used in predetermined amount in order that the aluminum ultimately will react with the total oxide in the dosing charge in order to form stable aluminum oxide. After formation, the aluminum oxide apparently deposits on the inner surface of the envelope 12. In

this manner, the aluminum oxide actually may improve the operating performance of the device since it forms a highly refractory protective layer between the quartz envelope and the reactive discharge.

As a specific example, 40 mg. of mercury and 13.6 mg. of mercury iodides are placed into the depending extension 24 of the tubulation 22, and 0.54 mg. of aluminum and 1.38 mg. of Sc O are placed into the arc tube 10. Any of the other indicated metals may be placed into the arc tube as oxides in gram-mole amount equivalent to the foregoing scandium oxide example, with the amount of aluminum which is added being calculated to ultimately react stoichiometrically with the total oxide in the dosing charge to form stable aluminum oxide.

When the completed lamp is initially operated, the aluminum will modify the discharge slightly as it reacts with the mercury halide to form aluminum halide. After a short period of operation, however, the formed aluminum halide will react with the metal oxide to form the desired metallic halide and the inert aluminum oxide. The ultimate conversion of aluminum to aluminum oxide will normally be completed in about two to twenty minutes of lamp operation.

As a possible alternative embodiment, there can also be dosed into the arc tube additional metallic halides, such as the iodides, which are relatively stable in the air. Examples of such stable halides are sodium iodide, or thallium iodide, or mixtures thereof. These stable iodides can thus be dosed initially into the arc tube with the air-stable metal oxides as specified hereinbefore, and upon operation of the device, the aluminum ultimately reacts with the oxide to convert the metal oxide to the iodide. As a specific example, 20 mg. of sodium iodide or 5 mg. thalliurn iodide, or a mixture thereof, are initially placed into the specific arc tube as described hereinbefore, along with the other dosing charge constituents.

As noted hereinbefore, the mercury charge which is introduced into the arc tube is predetermined in accordance with the voltage drop which is desired during operation of the device, and the method by which the amount of the mercury dosing charge is determined is well known in the art. Since the additive metal oxide, which will be present as the halide in the operating device, is normally used in amount which is greatly in excess over that amount which is needed, the amount of additive metal oxide which is dosed into the arc tube may vary over an extremely wide range. The amount of halogen, which is dosed into the arc tube as mercury halide, is generally predetermined in accordance with that amount of additive metal oxide which is used so that the halide will ultim-ately be formed during operation of the device, although an excess or deficiency of halogen, which varies from stoichiometry, may be used if desired.

It should be understood that any of the foregoing metal oxides, or any mixture thereof, can be closed into the arc tube, with or without additional metal halides which are stable in air and which require no special handling. Each metal oxide, when existing in the discharge as the halide, will provide a different effect, as will the combinations of the halides. Accordingly, a large number of different spectral effects can be obtained through dosing the arc tube in accordance with the present method.

While the specific example as described hereinbefore has considered the iodine dosing in detail, the present method can be used equally well to dose the arc tube with chlorides, or bromides, or mixtures thereof, with or without the iodides. As an example, to dose with chlorine or bromine, an equivalent gram-atom amount of same would be substituted for the iodine in the mercury iodide as given in the foregoing example. Alternatively, chlorine, bromine and iodine can be mixed in any proportions.

It will be recognized that the objects of the invention have been achieved by providing an improved method for dosing the arc tube portion of a mercury-additive type of discharge device with a desired metal which in the iodide form is unstable or hygroscopic in air, but which is stable in air in the oxide form.

As an alternative method for dosing the arc-sustaining filling into the arc tube, the envelope 12 can be evacuated and baked before any discharge-sustaining substance is dosed therein. This is readily accomplished by placing the discharge-sustaining substance into a capsule having an open end, with the loaded capsule secured in the tubulation. After baking, evacuating and gas filling the envelope 12, the tubulation is inverted to load the dosing charge from the capsule into the envelope.

While preferred embodiments of the invention have been illustrated and described hereinbefore, it is to be particularly understood that the present invention is not limited thereto or thereby.

I claim as my invention:

1. The method of dosing into the envelope of a substantially fabricated but unsealed arc-sustaining portion of a mercury-additive discharge device a predetermined amount of selected dosing substance which forms at least a part .of the total dosing charge to be dosed into said envelope, wherein said selected dosing substance includes selected metal in the oxide form, which selected metal is desired in said device as selected halide, said method comprising:

(a) placing into said envelope said dosing charge which includes:

(1) a predetermined amount of mercury which is at least partially chemically combined as mercury halide with a predetermined amount of the halogen component of said selected metal halide as desired in said device,

(2) a predetermined amount of said selected metal as air-stable oxide, and

(3) aluminum approximately in such amount as required ultimately to react with the total oxide in said dosing charge to form stable aluminum oxide; and

(b) sealing said envelope.

2. The method as specified in claim 1, wherein after said envelope is sealed off, said device is operated for a short time to cause said aluminum first to react with said mercury halide to form aluminum halide, and thereafter the formed aluminum halide reacts with said selected metal oxide to form aluminum oxide and said selected metal halide.

3. The method as specified in claim 1, wherein said aluminum has a large surface area.

'4; The method as specified in claim 1, wherein said selected mercury halide is mercury iodide.

5. The method as specified in claim 1, wherein said selected metal is closed into said envelope as a predetermined amount of at least one metallic oxide of the group consisting of thorium oxide, tantalum oxide, vanadium oxide, neodymium oxide, gadolinium oxide, uranium oxide, niobium oxide, yttrium oxide, samarium oxide, ytterbium oxide, europium oxide, indium oxide, terbium oxide, scandium oxide, holmium oxide, erbium oxide, pr-aseodymium oxide, titanium oxide, gallium oxide, hafnium oxide, iridium oxide, lanthanum oxide, magnesium oxide, cerium oxide, palladium oxide, rhenium oxide, rhodium oxide, ruthenium oxide and zinc oxide.

6. The method as specified in claim 1, wherein said dosing charge includes a predetermined pressure of selected inert, ionizable starting gas.

7. The method as specified in claim 1, wherein said dosing charge also includes a predetermined amount of additional selected metal halide which is stable in air.

8. The method as specified in claim 7, wherein said additional selected metal halide is at least one iodide of the group consisting of sodium iodide and thallium iodide.

9. The method as specified in claim 1, wherein said air-stable selected metal oxide and aluminum are first placed into said envelope, said envelope is then evacuated and baked to remove impurities therefrom, inert ionizable starting gas is then placed into said envelope, said mercury which is at least partially present as mercury halide is then introduced into said envelope, and finally said envelope is sealed.

10. The method as specified in claim 9 wherein:

(a) an elongated tubulation, which has a receptacle portion opening therein, connects to and opens into said envelope and said air-stable selected metal oxide and said aluminum are placed into said envelope through said elongated tubulation and said mercury which is at least partially combined with said halogen as mercury halide is positioned within the receptacle portion of said tubulation,

(b) said tubulation is connected to a vacuum system to evacuate same and said envelope is baked to remove substantially all impurities therefrom,

(c) an inert ionizable starting gas is introduced into said envelope through said tubulation,

(d) said tubulation is sealed at a point remote from its connection with said envelope,

(c) said mercury which is at least partially combined with said halogen as mercury halide is distilled from the receptacle portion of said tubulation and into said envelope, and

(f) said tubulation is tipped off at :a point proximate said envelope to seal said envelope.

References Cited UNITED STATES PATENTS 3,279,877 10/1966 Smith 3l6-24 2,029,144 1/1936 Wiegand 316-16 2,930,921 3/1960 Capeletti 316-16 RICHARD H. EANES, 111., Primary Examiner. 

